Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$94.34	11.355%	$105.0523	$105.05	$105.05	$105.10
Purchase #2	$37.95	6.251%	$40.3223	$40.32	$40.30	$40.30
Purchase #3	$235.82	13.503%	$267.6628	$267.66	$267.65	$267.70
Purchase #4	$207.64	7.139%	$222.4634	$222.46	$222.45	$222.50
Purchase #5	$245.83	5.669%	$259.7661	$259.77	$259.75	$259.80
Purchase #6	$92.57	9.623%	$101.478	$101.48	$101.50	$101.50
Purchase #7	$40.74	4.175%	$42.4409	$42.44	$42.45	$42.40
7 purchase totals =	$954.89		$1,039.1858	$1,039.18	$1,039.15	$1,039.30